The Science behind Radio

This week we begin posting a unit of lessons on audio drama for use in schools. They will eventually be gathered into a book but for now they are available freely here at www.weirdworldstudios.com . We hope you enjoy them and welcome any feedback you wish to provide.
We also offer a great line of audio drama scripts for sale (designed as a dinner party event but eminently suitable for use in classrooms). Our showcase contains a wide variety of FREE hand picked classic audio drama from the golden age of radio and the resources section of our site provides links to great resources on sound effects.

Enjoy!

Lesson 01

The Science Behind Radio.

This is the first lesson in our series on Radio and Audio Drama.

This lesson takes approximately 2 1/2 hours to complete. Add an extra 20 minutes for each practical activity attempted.

There are no pre-requisites for completing this lesson.

This booklet contains everything you need to complete this lesson. If you would like to complete the practical exercises you will also need…

1x 9 volt battery
1 x D cell battery
1x 1 meter of insulated copper wire
1x large (4-6 cm iron nail)
1 x thin sheet of aluminium foil
some iron filings/metal shavings (that can be picked up by a magnet).
a small piece of thin white card or paper.
3 x small (30 cm) lengths of copper wire
a small wireless radio receiver with antenna
a compass
a very sensitive volt meter

At the end of this lesson you will be able to…

explain how electro-magnetism allows a radio to operate
construct an electromagnet
transmit an electromagnetic signal to a receiver
explain how this signal can replicate sound waves

The Science Behind Radio

The invention of artificial magnets
How to build an electro-magnet
How iron is magnetised
How to view a magnetic field
How to build a basic transmitter
How a modern radio encodes and decodes sound

Antenna: A usually metallic device (as a rod or wire) for radiating or receiving radio waves.
Atoms: The smallest particles of an element that can exist either alone or in combination. Atoms in physics, while once believed to be the smallest particles in the universe have been discovered to be made up of even smaller particles (rendering their title something of a misnomer).
Capacitor: A device for storing electric charge.
Diaphragm: A thin flexible disk (as in a microphone or loudspeaker) that vibrates when struck by sound waves or that vibrates to generate sound waves.
Electricity: A fundamental form of energy observable in positive and negative forms that occurs naturally (as in lightning) or is produced (as in a generator) and that is expressed in terms of the movement and interaction of electrons.
Electro-magnet: A core of magnetic material surrounded by a coil of wire through which an electric current is passed to magnetize the core
Electro-magnetism: Magnetism developed by a current of electricity .
Electrons: A particle consisting of a charge of negative electricity.
Inductor: A part of an electrical apparatus that acts upon another or is itself acted upon by the process by which an electrical conductor becomes electrified when near a charged body.

Magnet: A body having the innate property of attracting iron and producing a magnetic field external to itself or a mass of iron, steel, or alloy that has this property artificially imparted.
Magnetic field: The portion of space near a magnetic body or a current-carrying body in which the magnetic forces due to the body or current can be detected.
Oscillator: An electrical component for producing alternating current; especially : a radio-frequency or audio-frequency generator.
Radio: The wireless transmission and reception of electric impulses or signals by means of electromagnetic waves particularly their conversion into sound.
Receiver: An apparatus for receiving radio or television signals.
Sine wave: A waveform that represents periodic oscillations in which the amplitude of displacement at each point is governed by a smooth mathematical relationship (proportional to the sine of the phase angle of the displacement).
Sound waves: Longitudinal pressure waves in any material medium regardless of whether they constitute audible sound; earthquake waves and ultrasonic waves are sometimes called sound waves.
Square wave: A waveform that varies periodically and abruptly from one to the other of two uniform values.
Transmitter: An apparatus for transmitting radio or television signals.

N/A

It is quite possible that, in this age of content-on-demand via the internet, radio (as a mass medium) has become an outmoded technology. Nonetheless radio waves are still important, even in this new digital world. All our wireless technologies (from mobile phones, to computer tablets, etc.) rely on radio technology. Understanding a little of the science and history behind radio technology gives us a key insight into the technologies that have become a part of our daily lives.

Before I was born my parents left their homes in Australia (separately as it happens) and went to work in India, where they in fact met and married. My father was involved in literacy programs and my mother was a nurse helping village women learn skills in hygiene and family health. After I was born there, (when I was four years old) my father fell seriously ill and the family moved back to Australia.

Until that time I had never encountered a radio or television. I still remember my fascination with the mysterious box out of which sounds came. The first radio I ever saw belonged to my grandparents and was a His Master’s Voice (HMV) Mantel radio. When I first heard it playing I thought it must be a trick and that my Grandfather was hiding in the room somewhere making the sounds (as far as I was concerned back then my grandfather could do anything). When that proved not to be the case, I theorised that there must be little people hiding inside the box who were doing all the talking. Fortunately my grandparents caught me before my plan to use a hammer to get the radio open was put into effect.

My grandfather, being the patient man that he was, and recognising that the questions were not going to go away, explained to me that the sounds were carried through the air from a radio station to the machine, ran down the antenna and came out of the speakers. I was still sceptical. Try as I might I couldn’t hear those sounds travelling through the air. Despite my uncertainty I was convinced my grandfather would never lie to me and that I just didn’t understand fully what was going on.

Most people who grow up in the presence of technology never stop to wonder how it works. It is taken for granted. However, those of us who encounter technology as something new and unfamiliar, often find ourselves marvelling at it and wondering how this amazing thing came to be and how it works.

As I grew older, I became a real fan of radio, particularly radio plays and audio drama. But I never lost that sense of curiosity regarding how the technology worked to begin with and this series of lessons aims to begin at the beginning, with a quick look at the science behind the magic.

Here are some questions to get you started…

What is your earliest memory of radio? Are there any key moments in your life that have been accompanied by the radio playing in the background?

Have you ever wondered about how radio works? What do you know already about the way radios operate? What would you like to know? Record your top three questions.

Have you ever used a baby monitor, walkie talkie or CB (citizen’s band) radio?

Radio shows are broadcast through the air. Some such as a baby monitor or walkie talkie can transmit over only a small distance. CB radio and other radio stations can transmit over much greater distances. Why do you think that is?

What about audio drama? Have you heard any radio plays or serials? If so, did you enjoy them? How do they differ from television?

The invention of artificial magnets

Radio, as we understand it today, was, like most technologies, the result of a series of scientific discoveries. These discoveries occurred largely in the field of electromagnetism. Understanding electro-magnetism is the key to understanding the underlying science behind radio since all radios utilise electro-magnetism.

The pioneer in this field was Michael Faraday, a physicist and chemist credited with the invention of the electric motor. It is arguable that he began the first real work on electromagnetism.

We say “arguable” because a lot of people were working on electro-magnetism at the same time and attempts to determine the identity of who was first are very difficult.

The key discovery regarding electro-magnetism occurred when Faraday observed that electricity, when passed through a wire, creates a magnetic field.

The theory of electromagnetism allows us, amongst other things, to construct artificial, temporary magnets. It may not be immediately obvious why this is so important to the development of radio, but stay with us for a little bit longer.

How to build an electro-magnet

Most of us have experienced permanent magnets – they are often used to affix notices to our fridges – but the discovery that you could create a magnet that could be switched on and off turned out to be remarkably useful.

An electro-magnet is basically created by running an electric current through a copper wire wrapped in a coil around a small piece of metal (such as an iron nail)

Try this yourself…

Grab a typical 9 volt battery, a long piece of insulated copper wire (approx. 1 meter/3.5 feet), an iron nail, a typical 1.5 volt D cell battery, some metal shavings, and a rolled up piece of aluminium foil (approximately the size of the nail).

Wrap the insulated copper wire (it will grow hot from the current so it needs to be insulated) around the nail to form a coil.

Warning: This creates a short circuit that can overload the battery. If the battery begins to grow hot, stop the experiment immediately.

When this is done, connect the two ends to the battery.

Presto, you’ve created an electromagnet. When the current is flowing (when both ends of the wire are attached to the battery) the nail becomes a magnet and will attract the metal shavings. Stop the current (disconnect a wire) and the nail returns to normal.

Here are some questions to consider…

What differences do you notice in the strength of the magnet…

when you wrap the nail tightly compared with loosely?

when you use more coils or less coils?

when you change the battery from a weaker battery to a more powerful battery?

when you replace the nail with a rolled up piece aluminium?

How iron is magnetised

To understand why these differences occur it also helps to understand a little about what is happening inside the iron nail. Different minerals are more or less easily penetrated by a magnetic field. Iron is very easily penetrated, aluminium is less easily penetrated, etc. A magnetic mineral has atoms that are all aligned and oriented in a single direction and exert a magnetic pull. Before the current is applied the atoms within the nail are arranged randomly – not pointing in any particular direction. When an electric current is introduced to the surrounding copper a magnetic field is created that begins realigning these atoms so that they all point in the one direction, exerting a magnetic pull. Increasing the strength of the current increases the strength of the magnetic field and so increases the number of atoms being realigned within the nail. An increase in the number of coils also increases the nails contact with the magnetic field created in the copper wire (again increasing the number of atoms being realigned) and if the copper wire is wound more tightly the number of atoms encountering the magnetic field increases again. The more the atoms
become aligned in this way, the greater the magnetic pull of the nail.

Of course, this doesn’t result in an infinite increase in magnetism within the nail. At a certain point, the number of atoms being realigned will have reached a maximum and the magnetic strength of the nail will go no higher.

When the electric current is removed the atoms within the nail return to their original state.

How to View a Magnetic Field

Would you like to see what magnetic field looks like?

Try this out…

Grab some iron filings, a sheet of blank white paper, and the electromagnet you created earlier.

Place a light dusting of iron filings on the sheet of paper. Hold the paper over the electro-magnet – make sure it is on. Move the paper close to the magnet and tap it lightly. The iron filings will realign and show you the shape of the magnetic field.

How to Build a Basic Transmitter

But what does all this have to do with radio?

Good question.

At their most basic, radio transmitters create and transmit changes in electromagnetic fields while radio receivers detect those changes.

Want to build an absurdly simple radio transmitter?

Try this out…

Grab a fresh 9 volt battery, a long piece (1 meter, 3.5 feet) of insulated wire, and an AM radio receiver.

Tune the radio receiver to some static. Take the battery and hold one end of the wire to one end of the battery. With the other end of the wire briefly scrape the surface of the other battery terminal, making sparks that will be visible in dim light. (Do not maintain a short circuit for more than a few seconds. If the battery begins to feel hot, cease the experiment.) Do this in really close proximity to the receiver’s antenna. The changes in the magnetic field caused by the passage of electricity through the wire are being detected by the radio. You can hear them as the crackle that occurs when you connect and disconnect the wire. The range is limited to a few centimeters, but you could tap out a Morse code message this way and broadcast it to the receiver.

Warning: This creates a short circuit that can overload the battery. If the battery begins to grow hot, stop the experiment immediately.

Here are some more questions to consider…

What happens as you move the battery and wire away from the antenna?

Why do you think this is?

What happens when you add a more powerful battery?

Why do you think the crackle in the receiver is detectable both when you connect and when you disconnect the current?

If you guessed that the antenna must be inside the magnetic field created by the battery in order to detect changes in the magnetic field you would be correct. You would also be correct if you guessed that as you increase the current running through the wire, you also increase the size of the magnetic field and its resultant range.
Lastly, you would be correct if you guessed that the antenna responds to ANY changes in the magnetic field around it (such as the magnetic field’s appearance and disappearance when the wire is connected to and disconnected from the terminals of the battery).

So, you can detect the transmission of alterations in a magnetic field using a radio receiver.

How a Modern Radio Encodes and Decodes Sound

To create radio in the modern sense you need two essential pieces of equipment; a radio transmitter and receiver.

As we have seen, sending an electric current through a wire creates a magnetic field. This field is strong enough to affect a compass. In fact, you can try this yourself…

Try this out…

Grab a 9 volt battery, a wire, and a compass.

Connect the wire to one of the battery’s terminals and run it under or beside the compass.

When you connect and remove the wire to the remaining terminal the magnetic field that is created will cause the compass to fluctuate.

We can take this experiment a bit further and use the magnetic field as a basic transmitter.

Grab a second wire and hook it up to a very sensitive voltmeter.

Place the wire about 5 cm from the original circuit.

By connecting the battery a current is created through the first wire. The current passing through the wire creates a magnetic field.

Watch what the voltmeter on the second wire shows when you connect and disconnect the battery.

If the second wire is close enough, the magnetic field surrounding the first wire should be large enough to overlap the second wire. Whenever the magnetic field in the first wire changes, a weak current briefly flows in the second. Note that the current flows when the magnetic field alters (not just when the circuit is closed). To keep the current going you need to keep changing the magnetic field. Connecting and reconnecting the battery makes these changes (creating and collapsing the magnetic field). The current in the second wire therefore only flows at these two moments.

A radio transmitter is the result of a rapidly changing electric current in a wire.

Rapidly connecting and disconnecting the battery creates what is known as a square wave. However, a much more useful wave to create is a sine wave (essentially because a sine wave has the same shape as a sound wave). By adding an oscillator to our circuit we can create a changing magnetic field that resembles a sine wave.

An oscillator is made out of two simple components; a capacitor and an inductor.

The capacitor stores power and allows current to flow until its storage capacity is full (while a current is flowing). When the current stops it discharges its store of electrons until it is empty (or a current flows again).

An inductor creates a magnetic field, resisting the flow of electrons through the wire until the field is built (storing energy as it does so) and then, if the current is turned off, releasing that energy until it is gone. If you were to charge up a capacitor and then (removing the battery) insert an inductor into the circuit the following would result…

The capacitor will start to discharge through the inductor. As it does, the inductor will create a magnetic field. Once the capacitor discharges, the inductor will try to keep the current in the circuit moving and charge up the capacitor. When the inductor’s field collapses the capacitor will attempt to discharge again.

This oscillation will continue until the circuit runs out of energy (at which point the capacitor will need to be recharged.

The oscillating magnetic field created in this way mimics a sine wave.

A radio transmitter modifies this magnetic sine wave to match a sound wave by using a microphone (a sensitive diaphragm that picks up sound vibrations in the air and translates them into an electric impulse that in turn is turned into an oscillating magnetic field). An antenna is used to transmit that wave to a radio receiver. The receiver contains a speaker (another sensitive diaphragm) that in turn picks up the oscillations in the magnetic field and vibrates at a rate creating waves in the air that our ears interpret as sound.

In our next lesson you’ll see how the invention of the radio was turned into the world’s second great mass medium (after printing of course).

What interesting side-effect occurs when an electric current is passed through a wire?

An electro-magnet has one major advantage over a permanent magnet. What is it?

Describe how an electromagnet is constructed.

What happens inside iron when it comes into close contact with a magnetic field.

Describe the construction of a basic radio transmitter.

Describe the components of an oscillator and how an oscillator makes it possible to encode and decode sounds in radio transmissions.

Label the diagram below (Battery, Receiver/Radio, Antenna, Ground, Microphone, Sine Wave, Oscillator)

Using all the labelled parts, describe how radio transmission is accomplished.

In ten minutes, brainstorm as many uses as you can for radio technology (from emergency services, through entertainment, to household uses).
See if you can come up with 30 or more.

How is an electromagnet constructed?

What happens to the atoms in an iron nail when it is magnetised?

How is the range of a magnetic field increased?

What occurs when a wire enters a magnetic field?

How can a magnetic field be manipulated to transmit a
detectable signal?

How does a radio translate sound waves into fluctuations in
a magnetic field?

For assessment:

Describe with examples how an artificial magnetic field can be created and modified to transmit a signal that can be detected and decoded as sound audible to the human ear.

Describe five modern uses for this technology.

(300 words)

The discovery and application of electro-magnetic fields has been one of the major technological advances of the modern age, essential to communications technology of all kinds from remote controls used in the home to wireless computing, to globe-spanning satellite communication. Understanding a little of how it works helps us to appreciate a little of the magic behind the machinery. But how did a simple means of transmitting and detecting changes in magnetic fields become one of the great mass mediums of human history? We’ll look at the answer to that question in our very next lesson.

The invention of artificial magnets that can be turned off and on has been incredibly useful for human communication and technology.

Increasing the energy to an antenna increases the range of a magnetic field.

An AM transmitter uses an oscillator to repeatedly weaken and strengthen a magnetic field into the shape of a sine wave and allows us to encode soundwaves into the field at varying frequencies.

These oscillations in the magnetic field can be detected by a receiver and turned back into sound waves audible to the human ear.

This technology was the basis for the world’s second great mass medium.

An ________ current passed through a conductive metal creates a ________ field. Changes occurring in a magnetic field can be detected by wires that come in contact with that field. This is the basis of _____ broadcasting. The more power used, the _______ the extent or range of the field. By __________ the field to match the variance of a ____ wave, sound waves can be encoded and decoded that are detectable by the human ear.

(sine, magnetic, electric, oscillating, radio, greater)

In our next lesson we will look at the history of commercial and public radio. We will discover how an area of esoteric interest among a handful of scientists was transformed into one of the major mass mediums of human history.

Lessons

Worked Example (Radio Adaptation of Rapunzel)

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Lesson 01